Glucocorticoid receptor (DlGR1) is expressed in pre-larval and larval stages of the teleost fish Dicentrarchus labrax

Glucocorticoid hormone receptors (GR), members of the nuclear hormone receptor superfamily, are ligand-dependent transcription factors expressed in various tissues by binding to specific DNA sequences. Since glucocorticoids have a role in maintaining the homeostatic status in fish, we previously cloned and sequenced a GR (DlGR1) of adult Dicentrarchus labrax; we also showed mRNA expression (in situ hybridization) and tissue immunohistochemical localization of DlGR1 in several organs. This work has now been extended to the examination of the expression, tissue distribution, and cytolocalization of DlGR1 in larval developmental stages by similar methods to those used for the adult organs. The riboprobe included the DlGR1 cDNA transcriptional activation domain (1.0–1,300 nucleotide sequence) showing no significant similarity with a known second GR cDNA sequence of sea bass. The antibody was specific for an opportunely selected peptide sequence of the DlGR1 transcriptional domain. In histological sections of brain, head kidney, gills, liver, anterior intestine, and spleen cells, the riboprobe was mainly located in the cell nucleus. The antibody identified DlGR1 in the head kidney, gills, liver, and anterior intestine, mainly located in the cytosol. These results are in agreement with the receptor location in adult tissues. The greater presence of both the transcript and protein of DlGR1 in the late developmental stages suggests an increasing expression of this receptor. The cytolocalization (nuclear-cytosolic) and presumptive roles of DlGR1-containing tissues are discussed

Impact of Daily Thermocycles on Hatching Rhythms, Larval Performance and Sex Differentiation of Zebrafish

In the wild, water temperature cycles daily: it warms up after sunrise, and cools rapidly after sunset. Surprisingly, the impact of such daily thermocycles during the early development of fish remains neglected. We investigated the influence of constant vs daily thermocycles in zebrafish, from embryo development to sexual differentiation, by applying four temperature regimens: two constant (24°C and 28°C) and two daily thermocycles: 28:24°C, TC (thermophase coinciding with daytime, and cryophase coinciding with night-time) and 24:28°C, CT (opposite to TC) in a 12:12 h light:dark cycle (LD). Embryo development was temperature-dependent but enhanced at 28°C and TC. Hatching rhythms were diurnal (around 4 h after lights on), but temperature- and cycle-sensitive, since hatching occurred sooner at 28°C (48 hours post fertilization; hpf) while it was delayed at 24°C (96 hpf). Under TC, hatching occurred at 72 hpf, while under CT hatching displayed two peaks (at 70 hpf and 94 hpf). In constant light (LL) or darkness (DD), hatching rhythms persisted with tau close to 24 h, suggesting a clock-controlled "gating" mechanism. Under 28°C or TC, larvae showed the best performance (high growth and survival, and low malformations). The sex ratio was strongly influenced by temperature, as the proportion of females was higher in CT and TC (79 and 83% respectively), contrasting with 28°C and 24°C, which led to more males (83 and 76%). Ovarian aromatase (cyp19a) expression in females was highest in TC and CT (6.5 and 4.6 fold higher than at 28°C, respectively); while anti-müllerian hormone (amh) expression in males increased in testis at 24°C (3.6 fold higher compared to TC) and particularly at 28°C (14.3 fold increase). Taken together, these findings highlight the key role of environmental cycles during early development, which shaped the daily rhythms in fish embryo and larvae, and ultimately influenced sex differentiation

Prenatal stress from trawl capture affects mothers and neonates:a case study using the southern fiddler ray (<i>Trygonorrhina dumerilii</i>)

Assessing fishing effects on chondrichthyan populations has predominantly focused on 15 quantifying mortality rates. Consequently, sub-lethal effects of capture stress on the 16 reproductive capacity of chondrichthyans are largely unknown. We investigated the 17 reproductive consequences of capture on pregnant southern fiddler rays (Trygonorrhina 18 dumerilii) collected from Swan Bay, Australia, in response to laboratory-simulated trawl 19 capture (8 h) followed immediately by air exposure (30 min). Immediately prior to, and for 20 up to 28 days post trawling, all females were measured for body mass (BM), sex steroid 21 concentrations (17-β estradiol, progesterone, testosterone) and granulocyte to lymphocyte 22 (G:L) ratio. At parturition, neonates were measured for total length (TL), BM and G:L ratio. 23 Trawling reduced maternal BM and elevated the G:L ratio for up to 28 days. Trawling did not 24 significantly affect any sex steroid concentrations relative to controls. Neonates from trawled 25 mothers were significantly lower in BM and TL than control animals, and had an elevated 26 G:L ratio. Our results show that capture of pregnant T. dumerilii can influence their 27 reproductive potential and the fitness of neonates. We suggest other viviparous species are 28 likely to be similarly affected. Sub-lethal effects of capture, particularly on reproduction, 29 require further study, particularly reproduction, to improve fisheries management and 30 conservation of chondrichthyan species.Fil: Guida, L.. Monash University; AustraliaFil: Awruch, Cynthia Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; Argentina. University of Tasmania; AustraliaFil: Waker, T.. Monash University; AustraliaFil: Reina. R.. Monash University; Australi